1) Field of the Invention
The present invention relates to an orthogonal excitation-type laser oscillator which outputs a laser beams having stable output or stable beam mode.
2) Description of the Related Art
A gas laser oscillator generally includes a discharge tube and an optical resonator. Gas (xe2x80x9claser gasxe2x80x9d) is filled is the discharge tube. The optical resonator has two mirrors. One mirror is arranged on one side of the discharge tube. The gas laser oscillator excites a laser by means of discharge in the laser gas. Large amount of heat is generated in the discharge tube at the time of laser oscillation. A part of this heat is transmitted to the optical resonator and a base plate which supports the discharge tube and the optical resonator. The optical resonator and the base plate get deformed because of this heat. As a result, an error of the parallelism of a pair of optical bases composing the optical resonator, displacement between an axis of the optical resonator and an axis of the oscillator housing and the like occur. Moreover, as for the optical resonator itself, a thermal expansion difference is generated between components such as a frame bar member and an end surface plate member due to a change in the outer temperature, and thus there is a fear that displacement of the optical resonator or the like occurs due to the thermal expansion difference. The displacement of the optical resonator causes an error of mirror alignment, and this makes the laser output and the beam mode of a laser beam unstable. Therefore, in order to cope with the displacement of the optical resonator and the like due to an influence of heat, laser oscillators having various structures are suggested.
FIG. 9 shows a perspective view of a conventional orthogonal excitation-type laser oscillator that has been disclosed in the Japanese Patent Application Laid-Open No. 2000-183425. In this oscillator, a front optical base 9 and a rear optical base 7 are provided on the sides of an oscillator housing 1. A partial reflection mirror is fixed to the front optical base 9 and a total reflection mirror is fixed to the rear optical base 7. The front optical base 9 and the rear optical base 7 are connected firmly by one lower supporting bar and two upper supporting bars totaling to three supporting bars 112 through 114 extending to a laser beam advancing direction (optic axis direction) so that the partial reflection mirror and the total reflection mirror are fixed parallel with each other on the same optical axis. An optical resonator is constituted in such a manner.
Axially center portions of the supporting bars 113 and 114 on the upper side of the oscillator housing 1 are connected to a center portion of the optic axis direction on an upper surface of the oscillator housing 1 by brackets 120 and 121, respectively. The connection of the supporting bar 113 positioned on a blower side where thermal deformation is less to the oscillator housing 1 by means of the bracket 120 is a completely fixing connection, and the connection of the supporting bar 114 positioned on a high-temperature side to the oscillator housing 1 by means of the bracket 121 is a movable connection by a slide base 122 of which movements in the axial and heightwise directions are restricted. Namely, the bracket 121 can slide on the slide base 122 to the right-left direction as shown by an arrow. Connection of the lower supporting bar 112 is not made by the oscillator housing 1 and the bracket, but both ends of the supporting bar 112 are simply fixed to the optical bases 9 and 7. Laser beam passing sections between the oscillator housing 1 and the rear optical base 7 and between the oscillator housing 1 and the front optical base 9 are connected by bellows, respectively.
In the conventional oscillator, although a change in the positional relationship between the two optical bases 7 and 9 due to a temperature distribution of a laser medium gas can be suppressed by the supporting structure using the three supporting bars 112 through 114 and the brackets 120 and 121, countermeasures are not taken against the instance where the laser oscillator is installed in a place where the vibration-proof measurement is not sufficient. Namely, in the orthogonal excitation-type laser oscillator shown in the prior art, an external force is applied to the optical resonator by external oscillation, and a structure of the optical resonator is elastically deformed, and this causes an error of the mirror alignment.
Deformation of the orthogonal excitation-type laser oscillator due to oscillation from the outside will be explained with reference to FIGS. 9 through 11 exemplifying the instance where the orthogonal excitation-type laser oscillator shown in FIG. 9 is installed on an XY stage which has a function of locating a processing apparatus. FIGS. 10 and 11 show a state that the external force is applied to the optical resonator composing the orthogonal excitation-type laser oscillator. FIG. 10 shows the external force to be applied to the optical resonator, and FIG. 11 shows the state of a deformation of the optical resonator due to these external forces.
The orthogonal excitation-type laser oscillator is fixed onto the XY stage, not shown, by a leg 131 provided to a lower portion of the oscillator housing 1. As for the optical resonator, the supporting bars 113 and 114 on the upper portion of the optical resonator are connected at the upper portion of the oscillator housing 1 by the brackets 120 and 121, but the optical resonator is not connected onto the XY stage. Namely, the optical resonator is hung from the oscillator housing 1. Therefore, when the oscillator housing 1 receives an acceleration G to a laser emission direction due to a movement of the XY stage, since the connected positions between the optical resonator and the oscillator housing 1 is the positions of the brackets 120 and 121 provided to the upper supporting bars 113 and 114, respectively, a force FG is applied from the oscillator housing 1 to the positions of the optical resonator as shown in FIG. 10. Meanwhile, inertial forces FA and FB are generated in barycentres A and B of the two optical bases 7 and 9 composing the optical resonator. Moments are generated in the optical resonator by these forces FG, FA and FB, and the structure of the optical resonator is elastically deformed as shown in FIG. 11. As a result, the error of the mirror alignment occurs.
When the orthogonal excitation-type laser oscillator is not installed in a sufficient vibration-proof environment, the force FG which is generated due to the oscillation exerting upon the oscillator housing 1 and which is applied to the connected points between the oscillator housing 1 and the optical resonator and the inertial forces FA and FB which are applied to the barycenter of the optical resonator act to deform the optical resonator remarkably. Such a deformation of the optical resonator, namely, the error of the mirror alignment makes a laser output and a beam mode of a laser beam unstable.
The present invention has been achieved in order to solve the above problems. It is an object of this invention to provide an orthogonal excitation-type laser oscillator in which an optical resonator composed of a pair of optical bases arranged parallel and supporting bars can keep arrangement positions of the paired optical bases constant regardless of forces to be applied to an oscillator housing due to oscillation.
In the orthogonal excitation-type laser oscillator according to the present invention, one optical base is provided on each side of a housing that houses a laser oscillator. Optical parts of an optical resonator are fixed to the optical bases. The optical bases are fixed to each other, independently from the housing, by supporting rods. First and second connecting members fix the respective optical base to respective end of the housing. The first connecting member bends in the direction of the laser beam when the housing deforms. The second connecting member attenuates oscillation generated due to the displacement of the housing.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings.